getrlimit setrlimit

介绍资源限制函数getrlimit, setrlimit，当然仍是man大法好。

1. 首先看下ulimit -a

wln@iZ232ngsvp8Z:~/2015/11> ulimit -a
core file size          (blocks, -c) unlimited
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 3827
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) 422620
open files                      (-n) 65535
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 3827
virtual memory          (kbytes, -v) 397760
file locks                      (-x) unlimited

2. 测试程序

#include <sys/time.h>
#include <sys/resource.h>
#include <stdio.h>

int limitArray[]={
  RLIMIT_AS,
  RLIMIT_CORE,
  RLIMIT_CPU,
  RLIMIT_DATA,
  RLIMIT_FSIZE,
  RLIMIT_MEMLOCK,
  RLIMIT_MSGQUEUE,
  RLIMIT_NICE,
  RLIMIT_NOFILE,
  RLIMIT_NPROC,
  RLIMIT_RSS,
  RLIMIT_RTPRIO,
  RLIMIT_LOCKS,
  //RLIMIT_RTTIME,
  RLIMIT_SIGPENDING,
  RLIMIT_STACK
};


int main()
{
  struct rlimit *limit;
  int len=sizeof(limitArray)/sizeof(int);
  int i=0;
  while(i<len)
  {
      if(getrlimit(limitArray[i],limit) != 0)
      {
        printf("%d %m\n",i);
      }
      else
      {
         printf("%2d: cur:%d  %d\n",i,limit->rlim_cur,limit->rlim_max);
      }
      i=i+1;
  }

  //set core limit
  limit->rlim_cur = RLIM_INFINITY;
  limit->rlim_max = RLIM_INFINITY;
  if(setrlimit(RLIMIT_CORE, limit) !=0)
  {
    printf("set limit failed %m\n");
  }
  else
  {
    printf("set limit ok\n");
  }
 
}

执行结果：

wln@iZ232ngsvp8Z:~/2015/11> ./getrlimit1
 0: cur:407306240  -1
 1: cur:-1  -1
 2: cur:-1  -1
 3: cur:-1  -1
 4: cur:-1  -1
 5: cur:65536  262144
 6: cur:819200  819200
 7: cur:0  0
 8: cur:65535  65535
 9: cur:3827  3827
10: cur:432762880  -1
11: cur:0  0
12: cur:-1  -1
13: cur:3827  3827
14: cur:8388608  -1
set limit ok

3. man

NAME
       getrlimit, setrlimit - get/set resource limits

SYNOPSIS
       #include <sys/time.h>
       #include <sys/resource.h>

       int getrlimit(int resource, struct rlimit *rlim);
       int setrlimit(int resource, const struct rlimit *rlim);

DESCRIPTION
       getrlimit() and setrlimit() get and set resource limits respectively.  Each resource has an associated soft and hard limit,
       as defined by the rlimit structure (the rlim argument to both getrlimit() and setrlimit()):

           struct rlimit {
               rlim_t rlim_cur;  /* Soft limit */
               rlim_t rlim_max;  /* Hard limit (ceiling for rlim_cur) */
           };

       The soft limit is the value that the kernel enforces for the corresponding resource.  The hard limit acts as a ceiling  for
       the  soft  limit:  an unprivileged process may only set its soft limit to a value in the range from 0 up to the hard limit,
       and (irreversibly) lower its hard limit.  A privileged process (under Linux: one with the CAP_SYS_RESOURCE capability)  may
       make arbitrary changes to either limit value.

       The  value RLIM_INFINITY denotes no limit on a resource (both in the structure returned by getrlimit() and in the structure
       passed to setrlimit()).

       resource must be one of:

       RLIMIT_AS
              The maximum size of the process's virtual memory (address space) in bytes.  This  limit  affects  calls  to  brk(2),
              mmap(2)  and  mremap(2), which fail with the error ENOMEM upon exceeding this limit.  Also automatic stack expansion
              will fail (and generate a SIGSEGV that kills the process if no alternate stack has been made available  via  sigalt-
              stack(2)).   Since  the  value is a long, on machines with a 32-bit long either this limit is at most 2 GiB, or this
              resource is unlimited.

       RLIMIT_CORE
              Maximum size of core file.  When 0 no core dump files are created.  When non-zero, larger  dumps  are  truncated  to
              this size.

       RLIMIT_CPU
              CPU  time  limit  in  seconds.   When  the process reaches the soft limit, it is sent a SIGXCPU signal.  The default
              action for this signal is to terminate the process.  However, the signal can be caught, and the handler  can  return
              control  to the main program.  If the process continues to consume CPU time, it will be sent SIGXCPU once per second
              until the hard limit is reached, at which time it is sent SIGKILL.  (This latter point describes Linux  2.2  through
              2.6  behavior.   Implementations  vary in how they treat processes which continue to consume CPU time after reaching
              the soft limit.  Portable applications that need to catch this signal should perform  an  orderly  termination  upon
              first receipt of SIGXCPU.)

       RLIMIT_DATA
              The maximum size of the process's data segment (initialized data, uninitialized data, and heap).  This limit affects
              calls to brk(2) and sbrk(2), which fail with the error ENOMEM upon encountering the soft limit of this resource.

       RLIMIT_FSIZE
              The maximum size of files that the process may create.  Attempts to extend a file beyond this limit result in deliv-
              ery of a SIGXFSZ signal.  By default, this signal terminates a process, but a process can catch this signal instead,
              in which case the relevant system call (e.g., write(2), truncate(2)) fails with the error EFBIG.

       RLIMIT_LOCKS (Early Linux 2.4 only)
              A limit on the combined number of flock(2) locks and fcntl(2) leases that this process may establish.

       RLIMIT_MEMLOCK
              The maximum number of bytes of memory that may be locked into RAM.  In effect this limit  is  rounded  down  to  the
              nearest  multiple  of  the system page size.  This limit affects mlock(2) and mlockall(2) and the mmap(2) MAP_LOCKED
              operation.  Since Linux 2.6.9 it also affects the shmctl(2) SHM_LOCK operation, where it sets a maximum on the total
              bytes  in shared memory segments (see shmget(2)) that may be locked by the real user ID of the calling process.  The
              shmctl(2) SHM_LOCK locks are accounted for separately from the per-process memory  locks  established  by  mlock(2),
              mlockall(2),  and mmap(2) MAP_LOCKED; a process can lock bytes up to this limit in each of these two categories.  In
              Linux kernels before 2.6.9, this limit controlled the amount of memory that could be locked by a privileged process.
              Since  Linux  2.6.9, no limits are placed on the amount of memory that a privileged process may lock, and this limit
              instead governs the amount of memory that an unprivileged process may lock.

       RLIMIT_MSGQUEUE (Since Linux 2.6.8)
              Specifies the limit on the number of bytes that can be allocated for POSIX message queues for the real  user  ID  of
              the calling process.  This limit is enforced for mq_open(3).  Each message queue that the user creates counts (until
              it is removed) against this limit according to the formula:

                  bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
                          attr.mq_maxmsg * attr.mq_msgsize

              where attr is the mq_attr structure specified as the fourth argument to mq_open(3).

              The first addend in the formula, which includes sizeof(struct msg_msg *) (4 bytes on Linux/i386), ensures  that  the
              user  cannot create an unlimited number of zero-length messages (such messages nevertheless each consume some system
              memory for bookkeeping overhead).

       RLIMIT_NICE (since Linux 2.6.12, but see BUGS below)
              Specifies a ceiling to which the process's nice value can be raised using setpriority(2)  or  nice(2).   The  actual
              ceiling for the nice value is calculated as 20 - rlim_cur.  (This strangeness occurs because negative numbers cannot
              be specified as resource limit values, since they typically have special meanings.  For example, RLIM_INFINITY typi-
              cally is the same as -1.)

       RLIMIT_NOFILE
              Specifies  a value one greater than the maximum file descriptor number that can be opened by this process.  Attempts
              (open(2), pipe(2), dup(2), etc.)  to exceed this limit yield the error EMFILE.  (Historically, this limit was  named
              RLIMIT_OFILE on BSD.)

       RLIMIT_NPROC
              The  maximum  number of processes (or, more precisely on Linux, threads) that can be created for the real user ID of
              the calling process.  Upon encountering this limit, fork(2) fails with the error EAGAIN.

       RLIMIT_RSS
              Specifies the limit (in pages) of the process's resident set (the number of virtual pages resident  in  RAM).   This
              limit only has effect in Linux 2.4.x, x < 30, and there only affects calls to madvise(2) specifying MADV_WILLNEED.

       RLIMIT_RTPRIO (Since Linux 2.6.12, but see BUGS)
              Specifies  a  ceiling  on  the  real-time  priority that may be set for this process using sched_setscheduler(2) and
              sched_setparam(2).

       RLIMIT_RTTIME (Since Linux 2.6.25)
              Specifies a limit on the amount of CPU time that a process scheduled under a real-time scheduling policy may consume
              without  making  a blocking system call.  For the purpose of this limit, each time a process makes a blocking system
              call, the count of its consumed CPU time is reset to zero.  The CPU time count is not reset if the process continues
              trying to use the CPU but is preempted, its time slice expires, or it calls sched_yield(2).

              Upon  reaching  the soft limit, the process is sent a SIGXCPU signal.  If the process catches or ignores this signal
              and continues consuming CPU time, then SIGXCPU will be generated once each second until the hard limit  is  reached,
              at which point the process is sent a SIGKILL signal.

              The intended use of this limit is to stop a runaway real-time process from locking up the system.

       RLIMIT_SIGPENDING (Since Linux 2.6.8)
              Specifies  the  limit on the number of signals that may be queued for the real user ID of the calling process.  Both
              standard and real-time signals are counted for the purpose of checking this  limit.   However,  the  limit  is  only
              enforced  for sigqueue(2); it is always possible to use kill(2) to queue one instance of any of the signals that are
              not already queued to the process.

       RLIMIT_STACK
              The maximum size of the process stack, in bytes.  Upon reaching this limit, a SIGSEGV signal is generated.  To  han-
              dle this signal, a process must employ an alternate signal stack (sigaltstack(2)).

              Since Linux 2.6.23, this limit also determines the amount of space used for the process's command-line arguments and
              environment variables; for details, see execve(2).

RETURN VALUE
       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

ERRORS
       EFAULT rlim points outside the accessible address space.

       EINVAL resource is not valid; or, for setrlimit(): rlim->rlim_cur was greater than rlim->rlim_max.

       EPERM  An unprivileged process tried to use setrlimit() to increase a soft or hard limit above the current hard limit;  the
              CAP_SYS_RESOURCE  capability  is required to do this.  Or, the process tried to use setrlimit() to increase the soft
              or hard RLIMIT_NOFILE limit above the current kernel maximum (NR_OPEN).

CONFORMING TO
       SVr4, 4.3BSD, POSIX.1-2001.  RLIMIT_MEMLOCK and RLIMIT_NPROC derive from BSD and are not specified  in  POSIX.1-2001;  they
       are  present  on the BSDs and Linux, but on few other implementations.  RLIMIT_RSS derives from BSD and is not specified in
       POSIX.1-2001;  it  is  nevertheless  present  on  most  implementations.   RLIMIT_MSGQUEUE,   RLIMIT_NICE,   RLIMIT_RTPRIO,
       RLIMIT_RTTIME, and RLIMIT_SIGPENDING are Linux-specific.

NOTES
       A child process created via fork(2) inherits its parent's resource limits.  Resource limits are preserved across execve(2).

       One can set the resource limits of the shell using the built-in ulimit command (limit in  csh(1)).   The  shell's  resource
       limits are inherited by the processes that it creates to execute commands.

BUGS
       In  older  Linux kernels, the SIGXCPU and SIGKILL signals delivered when a process encountered the soft and hard RLIMIT_CPU
       limits were delivered one (CPU) second later than they should have been.  This was fixed in kernel 2.6.8.

       In 2.6.x kernels before 2.6.17, a RLIMIT_CPU limit of 0 is wrongly treated as "no limit" (like RLIM_INFINITY).  Since Linux
       2.6.17, setting a limit of 0 does have an effect, but is actually treated as a limit of 1 second.

       A kernel bug means that RLIMIT_RTPRIO does not work in kernel 2.6.12; the problem is fixed in kernel 2.6.13.

       In  kernel 2.6.12, there was an off-by-one mismatch between the priority ranges returned by getpriority(2) and RLIMIT_NICE.
       This had the effect that actual ceiling for the nice value was calculated as  19 - rlim_cur.   This  was  fixed  in  kernel
       2.6.13.

       Kernels  before  2.4.22  did  not  diagnose  the  error  EINVAL  for  setrlimit()  when  rlim->rlim_cur  was  greater  than
       rlim->rlim_max.

SEE ALSO
       dup(2), fcntl(2), fork(2), getrusage(2), mlock(2), mmap(2), open(2), quotactl(2),  sbrk(2),  shmctl(2),  sigqueue(2),  mal-
       loc(3), ulimit(3), core(5), capabilities(7), signal(7)

COLOPHON
       This  page  is  part  of  release 3.15 of the Linux man-pages project.  A description of the project, and information about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

4.推荐阅读

1.getrlimit和setrlimit函数

http://bbs.chinaunix.net/thread-1940558-1-1.html